Gas processing unit and method of operating the same

ABSTRACT

A plant ( 1 ) and a gas processing unit (GPU) ( 17 ) of the plant can be configured to operate in accordance with a method that is configured to permit the GPU ( 17 ) to operate such that the optimum operating point for the GPU ( 17 ) at steady state to produce liquid carbon dioxide product from a separation unit ( 117 ) of the GPU ( 17 ) for sending to a storage device ( 19 ) is achieved with a desired purity level while simultaneously maintaining a required minimum carbon capture rate with the minimum consumption of power and/or minimum economic cost associated with operations of the GPU ( 17 ). A controller ( 23 ) can be configured to communicate with elements of the GPU ( 17 ) to receive parameter values to calculate manipulated variables configured to bias set points for parameters used to control operations of different elements of the GPU ( 17 ).

FIELD

The present disclosure relates to a combustion system such as a powergeneration system that utilizes at least one gas processing unit as wellas a control system for such a combustion system, and methods ofoperating the same.

BACKGROUND

Energy production systems that burn coal to produce power may include aboiler and a turbine. Energy production systems that are utilized inelectricity production and other components of such systems aredescribed, for example, in U.S. Patent Application Publication Nos.2014/0106284, 2014/0065560, 2014/0065046, 2014/0026613, 2014/0004028,2013/0315810, 2013/0298599, 2013/0291719, 2013/0255272, 2013/0205827,2013/0167583, 2012/0052450, 2012/0145052, 2010/0236500, and 2009/0133611and U.S. Pat. Nos. 7,954,458 and 6,505,567, European Patent ApplicationPublication No. EP 2 497 560, and International Publication Nos. WO2013/144853, WO 2013/057661, WO 2013/027115, WO 2013/024339, and WO2013/024337.

For example, in U.S. Patent Application Publication No. 2012/0145052, itis disclosed that some oxy-combustion systems may include an airseparation unit, a boiler, an air pollution control system, and a gasprocessing unit for separating carbon dioxide from flue gas. The heatfrom the flue gas of the boiler may be captured by steam, which is thenused to drive a steam turbine generator to produce electricity. The fluegas may then be processed to remove certain pollutants (e.g. NO_(x),SO_(x), etc.) and a portion of the treated flue gas may then be recycledto the boiler to effect combustion.

SUMMARY

According to aspects illustrated herein, there is provided a method ofoperating a plant having a gas processing unit that includes the caninclude the steps of determining parameter values associated withoperations of the gas processing unit, utilizing the parameter valuesassociated with the operations of the gas processing unit to determinebiasing values for biasing set points used to control operations ofelements of the gas processing unit, and sending the biasing values foradjusting the set points.

According to other aspects illustrated herein, an apparatus can includea gas processing unit, a controller having a processor connected tonon-transitory memory, and a model predictive control program stored inthe memory. The gas processing unit can be configured to connect to acombustion unit such that flue gas emitted from the combustion unit willbe fed to the gas processing unit. The gas processing unit can beconfigured to separate carbon dioxide from the flue gas to capture thecarbon dioxide from the flue gas. The controller can be communicativelyconnected to the gas processing unit to control operations of the gasprocessing unit with the model predictive control program.

The above described and other features are exemplified by the followingfigures and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of an apparatus, a plant, and associated exemplarymethods are shown in the accompanying drawings. It should be understoodthat like reference numbers used in the drawings may identify likecomponents, wherein:

FIG. 1 is a block diagram of a first exemplary embodiment of a plant.

FIG. 2 is a block diagram a first exemplary embodiment of the gasprocessing unit of the first exemplary embodiment of the plant.

FIG. 3 is a block diagram illustrating an exemplary embodiment of acontroller of the first exemplary embodiment of the plant.

FIG. 4 is a schematic diagram illustrating an exemplary model structurefor the exemplary embodiment of the controller of the first exemplaryembodiment of the plant.

Other details, objects, and advantages of embodiments of the innovationsdisclosed herein will become apparent from the following description ofexemplary embodiments and associated exemplary methods.

DETAILED DESCRIPTION

Referring to FIGS. 1-4, a plant 1 can be configured as an industrialplant, power plant, or electricity generation plant. The plant 1 can beconfigured to include a combustion unit. The combustion unit can includea combustor such as a furnace or boiler that is configured to combust afossil fuel (e.g. coal, natural gas, etc.) or other type of fuel to formcombustion products (e.g. steam, carbon dioxide, carbon monoxide, etc.)at a temperature within a desired pre-specified temperature range. Steamemitted by the combustion unit can be utilized to generate electricityor otherwise provide thermal energy for conversion into a desired systemoutput. Flue gas emitted from the combustion process can be routedthrough a series of other devices configured to treat the flue gas priorto the flue gas being emitted from the plant. The treatment of the fluegas can be configured to help ensure that the emitted flue gas complieswith applicable emission regulations or otherwise meets a desired set ofdesign criteria.

In some embodiments, the plant 1 can be configured as an oxygen firedplant that is configured to generate electricity from the burning of afossil fuel. For example, some embodiments of the plant can beconfigured as an oxygen fired pulverized coal plant. As another example,other embodiments of the plant 1 can be configured as an oxygen firednatural gas plant.

An embodiment of the plant 1 can be configured to include an airseparation unit (ASU) 3 that is configured to separate oxygen from otherair components (e.g. nitrogen, carbon dioxide, etc.) and feed the oxygengas flow separated from the air to a mixer 5 via an oxygen feed conduitconnected between the ASU 3 and the mixer 5. The mixer 5 can beconfigured to mix the oxygen with at least one other recycled plantfluid flow to form an oxidant flow for feeding the oxidant flow of fluidto a combustion unit 9 via at least one oxidant flow feed conduitconnected between the mixer 5 and the combustion unit 9. In someembodiments, a portion of flue gas emitted by the combustion unit 9 canbe recycled back to the mixer 5 for mixing with the oxygen from the ASU3 to form the oxidant flow.

A fuel source 7 can be connected to a combustion unit 9 for feeding fuelto the combustion unit. The fuel source 7 can be, for example, a coalmill that pulverizes coal for providing the coal to the combustion unit9 or can be another type of fuel source. The combustion unit 9 can beconfigured as a boiler such as an oxygen fired boiler, or can beconfigured as a furnace or other type of combustor.

The combustion unit 9 can be configured to combust the fuel from thefuel source 7 in the presence of the oxidant flow received from themixer 5 to produce steam and flue gas. The steam can be fed to a turbineof a generator or other power generation unit 11 via a steam transportconduit connected between the combustion unit 9 and the power generationunit 11. Flue gas formed in the combustion unit 9 can be separated fromthe steam and subsequently sent toward a number of flue gas treatmentdevices for treating the flue gas prior to recycling the flue gas withinthe plant and/or emitting a portion of the flue gas to the atmosphereexternal to the plant 1.

For instance, the flue gas from the combustion unit 9 can be transportedto a particulate collector unit 13 via a particulate collector unit fluegas feed conduit connected between the particulate collector unit 13 andthe combustion unit 9. The particulate collector unit 13 can beconfigured as a dust eliminator, a particulate filter, or other type ofparticulate removal device. The particulate collector unit 13 can beconfigured to separate fly ash and other particulates from the flue gasreceived from the combustion unit 9.

After the flue gas is treated by the particulate collector unit 13, thetreated flue gas can be sent to a desulfurization unit 15 that isconfigured to remove sulfur oxides from the flue gas. Thedesulfurization unit 15 can be configured as a dry flue gasdesulfurization system or a wet flue gas desulfurization system, forexample. The desulfurization unit 15 can receive the flue gas from theparticulate collector unit 13 via a desulfurization unit feed conduitconnected between the desulfurization unit 15 and the particulatecollector unit 13.

After the flue gas is treated by the desulfurization unit 15, it can befed to a gas processing unit (GPU) 17 via a GPU feed conduit connectedbetween the desulfurization unit 15 and the GPU 17. Prior to being fedto the GPU 17, the flue gas can be split into a first portion and asecond portion. The first portion of the flue gas can be recycled to themixer 5 for mixing with oxygen from the ASU 3 to form the oxidant flowfor feeding to the combustion unit 9. The second portion of the flue gascan be transported to the GPU 17 via the GPU feed conduit.

The GPU 17 can be configured to remove a substantial portion of carbondioxide from the flue gas to capture that carbon dioxide and output afluid that is substantially composed of carbon dioxide for storage,further purification, or other distribution. The GPU 17 can beconfigured to feed a first portion of the flue gas treated by the GPU 17to have a substantially lower portion of carbon dioxide to anotherdevice 25 for further processing or for emitting to the atmosphere afterthe GPU 17 has processed that flue gas. For instance, the device 25 canbe a stack or heat recovery steam generator (HRSG) that is connected tothe GPU 17 for receiving the first portion of treated flue gas via anoutlet conduit connected between device 25 and GPU 17. A second portionof the flue gas treated by the GPU 17 can be distributed to the fuelsource 7 for being used in operations for treating the fuel prior tofeeding the fuel to the combustion unit 9. A fuel source conduit 21 canbe connected between the GPU 17 and fuel source 7 for recycling thatsecond portion of the flue gas after that gas was treated by the GPU 17.

The fluid substantially composed of carbon dioxide generated by thetreatment of the flue gas performed by the GPU 17 can be output to astorage device 19 or other type of processing device via a carbondioxide fluid output conduit connected between the GPU 17 and storagedevice 19. The substantially pure carbon dioxide fluid may be stored ina storage device 19 or other type of vessel. The substantially purecarbon dioxide containing fluid can be composed of 80-100 molar percentcarbon dioxide or greater than 70 molar percent carbon dioxide for someembodiments of the plant. For instance, some embodiments of the plantcan be configured so that the substantially pure carbon dioxidecontaining fluid output by the GPU 17 can be between 92-98 molar percentcarbon dioxide.

In some embodiments, the substantially pure carbon dioxide containingfluid stored in the storage device 19 can also be subsequently processedfurther for forming a product to be distributed to a vendor that desiressuch a compound. In other embodiments, that fluid may be stored for arelatively long period of time for sequestration of the carbon dioxide.

At least one controller 23 can be communicatively connected to the ASU3, the mixer 5, the fuel source 7, the combustion unit 9, the powergeneration unit 11, the particulate collector unit 13, thedesulfurization unit 15, the GPU 17 and device 25 as indicated by thebroken line arrows in FIG. 1. The controller 23 can also becommunicatively connected to conduit elements connected between suchdevices, valves, proportional-integral-derivative controllers, andmeasurement sensors such as flow sensors, temperature sensors, andpressure sensors connected to portions of conduits or portions of theGPU 17, device 25, combustion unit 9, ASU 3, fuel source 7, mixer 5,power generation unit 11, particulate collector unit 13, anddesulfurization unit 15 as indicated by broken line arrows in FIGS. 1and 2 such that the controller 23 can receive information relating toone or more parameters of operation of the plant 1 and/or operation ofGPU 17.

The controller 23 can be an electronic device such as a computer,workstation, computer device, or other type controller. The controller23 can include at least one non-transitory memory 201, at least onetransceiver unit 203 that can include at least one receiver and at leastone transmitter configured for communicating with other devices to whichthe controller 23 is communicatively connected, and at least oneprocessor 205 connected to the memory 201 and transceiver unit 203. Thetransceiver unit 203 can also be configured to permit the controller 23to communicate with remote devices via a network connection such as theinternet or an intranet. The processor 205 can be a central processingunit, a microprocessor, or other type of hardware processor elementconfigured to run one or more applications stored on the memory 201 suchthat the controller 23 is able to perform a method defined by code orother instructions of those one or more applications stored in thememory 201. For instance, the controller 23 can have a model predictivecontrol program stored in the memory 201 of the controller 23 that canbe run by the processor 205 to control operations of the GPU 17 and/orplant 1.

As can be appreciated from FIG. 2. The GPU 17 can include a coolingdevice 101 such as direct contract cooler (DCC) or other type of coolingdevice that is configured to cool flue gas received from thedesulfurization device 15. Cooling water can be fed from a source ofwater 103 to the cooling device 101 via a cooling water feed conduit sothat the water can be used to cool the flue gas to a temperature that iswithin a pre-specified temperature range that is cooler than thetemperature the flue gas was at when it was initially fed to the coolingdevice 101. The cooling water from the source of water 103 can be mixedwith glycol or other refrigerant or otherwise exposed to such arefrigerant to help the water be within a desired pre-specifiedtemperature range for providing a desired amount of heat transfer ofheat from the flue gas to the water as the water passes through thecooling device 101.

The water output from the cooling device 101 can be warmer than thewater fed to the cooling device 101. The output water can be fed to afirst water collecting device 105 a via a water output conduit connectedbetween the cooling device and the first water collecting device 105 afor subsequently being routed to another device for use of the heat ofthe warmer water or for sending to a tank for the water to betemporarily stored until being reused for another plant process or GPUprocess.

The cooled flue gas can be output from the cooling device and fed to aflue gas compressor system 107 via a flue gas compressor system feedconduit connected between the compressor system 107 and the coolingdevice 101. The flue gas compressor system 107 can be a one stagecompressor system, two-stage compressor system, three-stage compressorsystem, or other type compression system utilizing one or morecompressors to compress the flue gas to a desired pressure. After eachcompressor stage, the compressed flue gas can be passed through acooling device for cooling the flue gas to a desired temperature priorto being fed to another compressor for further compression or prior tobeing fed to a purifier unit 109 for purifying the compressed flue gas.Water from at least one source of water can be fed to heat exchangersfor use as a cooling fluid for the heat exchangers positioned betweencompressor stages or positioned between the last compressor stage andthe purification unit 109 for cooling the compressed flue gas to atemperature within a pre-specified temperature range. Water that isheated from its use in such heat exchangers of the flue gas compressorsystem 107 can be transported from the heat exchangers to a second watercollecting device 105 b. In some embodiments, the first and second watercollecting devices can be separate vessels or can be conduits that feedwater to the same storage vessel for that water to be temporarily storedfor further use or processing of the plant 1 or GPU 17.

After being compressed to a desired pressure that is within apre-specified pressure range by the flue gas compressor system 107 theflue gas can be transported to a purification unit 109 via apurification unit feed conduit connected between the flue gas compressorsystem 107 and the purification unit 109. The purification unit 109 canbe configured to remove undesirable components within the flue gas. Forinstance, the purification unit 109 can be a mercury adsorber that isconfigured to utilize activated carbon to remove mercury and otherundesired heavy metals or other compounds from the flue gas passingthrough the purification unit 109. The purification unit 109 can also beconfigured to utilize at least one absorption mechanism, other types ofadsorption mechanisms or combinations of adsorption and absorptionmechanisms for removing pre-specified components from the flue gas.

After being passed through the purification unit 109, the purified fluegas can be transported to a dryer unit 111 to dry the flue gas via adryer unit feed conduit connected between the purification unit 109 andthe dryer unit 111. The flue gas can be dried in the dryer unit so thatthe flue gas has a humidity level that is at a pre-selected value thatis below the dew point of the lowest temperature in a condenser unit 115that is downstream of the dryer unit 111 to prevent condensation orfreezing of water in the condenser unit 115.

A regeneration unit 113 can receive a flow of heated, drying fluid thatwas passed through the dryer unit 111 to dry the flue gas. The heateddrying fluid can be transported from the dryer unit 111 to theregeneration unit 113 via a regeneration unit feed conduit connectedbetween the dryer unit 111 and the regeneration unit 113. In someembodiments, the dryer unit 111 can be configured so that the dryingfluid is routed vertically upwards through a depressurized exhausteddryer bed prior to being sent to a device 25 (e.g. stack and/or HRSG)for subsequent emission to the atmosphere. After being regenerated, atleast a portion of the regenerated fluid emitted from the regenerationdevice can be transported to the device 25 for emission to theatmosphere.

As indicated by the broken line arrow shown in FIG. 2, the drying fluidcan include off gas from a separation unit 117 that is passed through acondenser unit 115 and is subsequently passed through the dryer unit 111as a drying fluid. The off gas from the separation unit 117 can betransported through the condenser 115 and dryer unit 111 via an off gasrecycle conduit connected between the separation unit 117 and the dryerunit 111. After being regenerated in the regeneration unit 113, thedrying fluid can be fed to device 25 via an off gas feed conduitconnected between device 25 and regeneration unit 113. After passingthrough device 25, the drying fluid can be emitted to the atmospherethat is external to the plant 1.

The dried flue gas can be transported from the dryer unit 111 to thecondenser unit 115 that is configured to cool the flue gas to condensethe dried, purified flue gas. The condenser unit 115 can be configuredas a carbon dioxide condenser for condensing the carbon dioxide as aliquid flow while other elements within the flue gas remain a gas. Inone embodiment, the condenser unit 115 can be configured as a cool boxthat is configured to cool the flue gas and condense it in multiplesequential steps or in a parallel processing of subdivided flows of theflue gas using plate heat exchangers. In some embodiments, the condenserunit 115 can be configured so that a final output temperature of thefluid output from the condenser unit 115 is within a pre-specifiedtemperature range (e.g. −50° C. or within a range of −40° C. to −60° C.)by using the coldness of evaporation of liquid carbon dioxide supportedby a stepwise expansion of the residual uncondensed flue gas.

The condensed liquid and remaining gas from the condensed flue gas aresubsequently fed from the condenser unit 115 to a separation unit 117via a carbon dioxide separation unit feed conduit. The separation unit117 is configured to separate the substantially carbon dioxide liquid(e.g. liquid that is between 80-100 mole percent carbon dioxide, liquidthat is more than 70 mole percent carbon dioxide, or liquid that isbetween 92-98 mole percent carbon dioxide, etc.) received from thecondenser unit 115 from the non-condensed gas. The separation unit 117can include one or more separation columns for receiving the condensedfluid from the condenser unit 115 as well as one or more expanders forexpanding off gas separated from the condensed liquid by the separationcolumns. The separation columns of the separation unit 117 can beconfigured to operate in parallel or in series.

The separated substantially carbon dioxide fluid is transported from theseparation unit 117 to a storage device 19 via a storage conduitconnected between the storage device 19 and the separation unit 117. Apump or series of pumps may be connected to the storage conduit forfacilitating the flow of substantially carbon dioxide fluid to thestorage device 19. During the transportation of the substantially carbondioxide fluid, the fluid may be transported such that it starts as aliquid but subsequently undergoes a phase change to a gas. For instance,the liquid can be compressed, otherwise pressurized, or heatedsufficiently so that the liquid changes phase into a gas or into amixture of a liquid and a gas. Alternatively, the storage device 19 canbe configured to facilitate such a phase change in the substantiallycarbon dioxide fluid received from the separation unit 117.

For instance, prior to being distributed to the storage device 19,portions of the separated carbon dioxide can be transported from theseparation unit 117 to the flue gas compressor system 107 for use as acooling fluid that is passed through inter stage heat exchangers used tocool compressed flue gas. For instance, a first portion of the carbondioxide fluid separated via the separation unit 117 can be transportedto a heat exchanger located between compressor stages of the flue gascompressor system 107. A second portion of the separated substantiallycarbon dioxide fluid can be transported via a portion of the storagefeed conduit to a heat exchanger that is between another stage ofcompressors or is located between the last compressor stage and thepurification unit 109.

The gas separated from the substantially carbon dioxide liquid condensedout of the flue gas can be referred to as off gas. The off gas caninclude inert elements within the flue gas (e.g. argon and nitrogen) aswell as oxygen and a portion of carbon dioxide that was not condensed inthe condenser unit 115 and/or otherwise separated from the rest of theflue gas. The separation unit 117 can be configured so that theseparated off gas can have a composition of between 20-40 mole percentcarbon dioxide, 15-25 mole percent oxygen, 5-15 mole percent argon,30-50 mole percent nitrogen, and between 0-1 mole percent of otherelements such as nitrogen oxides and/or sulfur oxides.

At least a first portion of the off gas can be transported from theseparation unit 117 through the condenser 115 and to the dryer unit 111for use in helping to cool the flue gas for facilitating condensing ofthe carbon dioxide from the flue gas passing through the condenser unit115 and subsequently for passing through the dryer unit 111 as a dryingfluid or part of the drying fluid. Recycling of the first portion of theoff gas can help improve efficient operation of the GPU 17. A secondportion of the off gas can be transported from the separation unit 117to the regeneration unit 113 to assist in regeneration of the dryingfluid after the heated drying fluid is emitted from the dryer unit 111.The second portion of the off gas can be transported to the regenerationunit via an off gas feed conduit connected between the separation unit117 and the regeneration unit 113. A third portion of the off gas can befed to the device 25 for subsequent use and/or emission to theatmosphere external to the plant 1 via an off gas output conduitconnected between the separation unit 117 and the device 25. A portionof the regenerated fluid output from the regeneration unit 113 can alsobe transported to the device 25 via regenerated fluid feed conduitconnected between the regeneration unit 113 and device 25 for emittingthat fluid to the atmosphere.

The controller 23 can be configured to control and/or monitor operationsof the plant 1 and/or GPU 17. The controller 23 can be configured to runa predictive model control program that is structured to configure thecontroller 23 to monitor and control operations of the GPU 17 to ensurethe GPU 17 operates to prevent formation of dry ice and/or water ice,minimize flue gas temperature deviations, maintain a rate at whichcarbon dioxide is captured out of the flue gas by the GPU 17 and enhanceoperating flexibility. If the plant 1 is configured as a power plant,the controller 23 can also be configured to enhance the ability of theplant to adjust to load changes via the predictive model controlprogram. The controller 23 can communicate with a computer device 31that is configured as a distributed control system to effect operationsof the plant 1 and GPU 17. Alternatively, the controller 23 can beconfigured such that it is a component of the distributed control systemor other control system such that the model predictive control is anapplication run on a computer of the control system that communicateswith other applications run on the controller 23 for providing controlof operations of the plant 1 and GPU 17.

As may be appreciated from FIG. 4, the controller 23 can be configuredto receive data from different elements of the GPU 17 and other plantdevices such as the ASU 3, combustion unit 9, and power generation unit11. The controller 23 can receive data from different sensors (e.g.temperature sensors, pressure sensors, flow rate sensors, fluidcomposition sensors, carbon dioxide concentration detectors, etc.) fromeach element of the GPU 17 as well as each element of the plant 1. Forexample, the controller can receive data relating to disturbancevariables (DVs) 301, controlled variables (CVs) 303, and constraintvariables (CTs) 305. The model predictive control program can bestructured to configure the controller 23 to determine parameter valuesassociated with operations of the GPU 17, utilize the parameter valuesassociated with the operations of the GPU 17 to determine biasing valuesfor biasing set points by which operations of elements of the GPU 17 arecontrolled, and send the determined biasing values to the GPU 17 foradjusting the set points when the model predictive control program isrun by the controller 23.

For example, the controller 23 can be configured to utilize a modelpredictive control process control algorithm defined by the code of themodel predictive control program to utilize data received from differentelements of the GPU 17 to determine biasing values for manipulatedvariables (MVs) 307 that can be subsequently sent to the distributedcontrol system and/or used by the distributed control system forcontrolling operations of the plant 1 and/or GPU 17. The calculatedbiasing values for the MVs can be provided to the distributed controlsystem to bias various set point values that are overseen by thedistributed control system for operations of the GPU 17 and/or plant 1.If the distributed control system is also an application run on thecontroller 23, then the biasing values for the MVs determined via themodel predictive control program can be fed to the one or moreapplications of the distributed control system for biasing set pointsused by that system.

Examples of a value for a DV 301 can include a flue gas flow rate, ademand for the load of the combustion unit (e.g. boiler load demand orfurnace load demand, etc.) and/or a feed-forward variable. Examples ofvalues for CVs can include carbon dioxide purity in the substantiallycarbon dioxide fluid output from the separation unit 117, the carbondioxide capture rate for operations of the GPU 17, the carbon dioxideconcentration of off-gas, the temperature of inlet gas fed to aseparator of the separation unit 117, or the inlet off gas temperatureof an expander of the separation unit 117 and/or condenser unit 115.Examples of values for CTs include inlet flue gas temperatures atdifferent stages or elements of the separation unit 117, outlet liquidtemperatures for the substantially carbon dioxide liquid output at oneor more stages of the separation unit 17 or different separation columnsincluded within the separation unit, and off gas expander outlettemperatures for off gas separated by separation columns of theseparation unit 117. In some embodiments, the CT values can be highlimit values and low limit values for different parameters of the GPUand/or plant 1 that are selected to ensure safe operation of the GPU 17or plant 1. An example of biasing values for MVs include biasing valuesfor parameters that are to be transmitted to the distributed controlsystem for use in biasing the set points of different parameters. Thebiasing values can be configured to bias separator carbon dioxide levelset points for separation columns of the separation unit 117,temperature set points for one or more of the separation columns, inletpressure set points for off gas expanders that receive off gas separatedfrom the liquid in the separation unit 117, compressor inlet pressureset points for different compressors of the plant 1 or GPU 17,compressor outlet pressures for one or more compressors of the GPU 17 orplant 1, and temperatures of fluids at the inlets or outlets ofcompressors of the GPU 17 and/or plant 1. The biasing values for MVs canbe determined based on the DVs, CTs, CVs, and any correlations that aredetermined to exist between these variables for a particular embodimentof the plant 1 and/or GPU 17. The correlations can be correlationsbetween different parameters that are developed from test data routinelygathered during the fabrication and commissioning of a plant as well asother correlations known to exist from mass and energy balance equationsrelating to operations of the GPU 17 and/or plant. The CTs, CVs, DVs,and biasing values for MVs that are utilized in a particular embodimentcan be any of a number of different parameters to meet a particulardesign objective of a particular embodiment of a plant or GPU.

If the distributed control system is run on another computer device 31(as shown in broken line in FIG. 1), then the controller 23 can becommunicatively connected to that other computer device 31 to transmitthe biasing values for the MVs to the computer device 31. The computerdevice 31 can have hardware elements such as non-transitory memory, atleast one transceiver unit, and at least one processor unit connected tothe memory and the transceiver unit for running one or more programsstored on the memory for running the distributed control system. Thebiasing values for the MVs the distributed control system computerdevice 31 receives from the controller 23 can be utilized by thecomputer device 31 to bias the set points associated with the biasingvalues for the MVs received from the controller 23 to adjust the setpoint values utilized for controlling operations of the GPU 17 and/orplant 1.

As an alternative, or in addition, the controller 23 can communicate thebiasing values for the MVs to proportional-integral-derivativecontrollers of the different elements of the GPU 17 and/or plant 1 tobias the set points of the proportional-integral-derivative controllersassociated with those MVs. For instance, the controller 23 cancommunicate a determined biasing value associated with a temperaturemonitored by a proportional-integral-derivative controller of theseparation unit 117 so that the proportional-integral-derivativecontroller adjusts the temperature set point used by thatproportional-integral-derivative controller. As another example, thecontroller can communicate a biasing value associated with a pressure orflow rate of an element of the GPU 17 or plant 1 to aproportional-integral-derivative controller of that element of the GPU17 or plant 1 to function as a supervisory controller to thatproportional-integral-derivative controller. By the controller 23providing a biasing value associated with the parameter to be controlledby that proportional-integral-derivative controller, the controller 23is able to provide input to effect an adjustment of a set point utilizedby the proportional-integral-derivative controller so that operations ofthe element to be controlled by that proportional-integral-derivativecontroller are adjusted based on the biasing value received from thecontroller 23.

In some embodiments, the controller 23 can be configured to maximize thecost effectiveness of the operations of the GPU 17 so that operations ofthe GPU 17 are adjusted to meet a particular operational objective of aplant 1 or GPU 17 operator. For instance, the controller 23 can beconfigured to operate to prevent problems associated with ice formationin the GPU 17 (e.g. water ice or dry ice) and minimize flue gastemperature deviations while also operating the GPU 17 to maximize theeconomic value of carbon capture at a desired purity of carbon productin view of the costs associated with operations of the GPU to capturethe carbon dioxide at the pre-specified purity levels. The effectregulatory compliance and/or the value of carbon credits that may berelevant to the operations of the GPU 17 and plant 1 can also beincluded within the variables weighed by the controller to determine thebiasing values for biasing set points for different parameters formaximizing the economic return that can be provided by operations of theGPU 17 and/or plant 1.

In some embodiments, the controller 23 can be configured to determinebiasing values for biasing set points used to control operations ofelements of the GPU 17 based on utilization of the formula:

J=Σ _(i=1) ^(N) ^(CV) α(CV_(i) ^(SP)−CV_(i) ^(PV))²+Σ_(j=1) ^(N) ^(CT)β(CT_(j) ^(lim)−CT_(j) ^(PV))²+Σ_(k=1) ^(N) ^(MV) γΔMV_(k) ²

Where,

-   -   CV_(i) ^(SP): the reference value of the i-th control variable        (e.g. required temperature set point)    -   CV_(i) ^(PV): the measured value of the i-th control variable        (e.g. measured temperature)    -   CT_(j) ^(lim): the limits of the j-th constraint variable (e.g.        separation unit 117 expander outlet temperature low limit)    -   CT_(j) ^(PV): the measured value of the j-th constraint variable        (e.g. separation unit 117 expander outlet temperature)    -   ΔMV_(k): the actual change of the k-th biasing value for the        k-th manipulated variable (e.g. separation unit 117 expander        inlet pressure set point biasing value)    -   α: weighting coefficients/matrix reflecting the relative        importance of the control variables    -   β: weighting coefficients/matrix reflecting the relative        importance of the constraint variables    -   γ: weighting coefficient penalizing relative large changes in        the biasing values for the manipulated variables        In other embodiments of the controller 23, alternative forms of        cost functions can include other parameters such as parameters        configured to represent penalty of constraint variable        violations. Additionally, linear cost terms of MVs, etc. can        also be incorporated in the calculations utilized by the        controller to determine MVs.

The biasing values for MVs determined by the controller 23 can beconfigured for sending to the distributed control system for adjustingor biasing set points that the distributed control system utilizes tocontrol operations of the plant and/or GPU 17. In determining thebiasing values for the MVs, the controller can be configure so that thevalues for DVs used in its calculations to determine biasing values forthe MVs can be parameter values that cannot be changed by the controller23 when performing its calculations. For each value of the CVs, thevalue of the CV can be affected by both the biasing value for at leastone MV and the value of at least one DV relating to that CV. For eachvalue of the CT, the process output can be controlled by the controller23 when determining biasing values for the MVs by adjusting the CTvalues within pre-specified limits (e.g. non-changeable high and lowlimits associated with a particular CT where the high and low limits areset for safety reasons and/or to ensure a desired operational life of aparticular capital asset included within the plant 1 and/or GPU 17). Forinstance, the flue gas flow that enters the GPU can be configured as afeedforward signal to the controller 23. The temperatures at certainpoints such as expander outlets can be selected so that thosetemperature values are constrained to prevent dry ice formation or waterice formation that can pose maintenance issues, reduce effectiveness ofthe GPU 17, and reduce the life of different elements of the GPU 17.Separation column levels, expander inlet pressures, or compressor inletpressures of the GPU 17 can be configured as manipulated variables thatcan be utilized to improve the transient response to differentconditions within the plant and also increase the carbon dioxide purityin the substantially carbon dioxide product formed from operations ofthe GPU 17.

Testing was conducted to assess the value that embodiments of thecontroller 23 can provide to operations of the GPU 17 and/or plant 1.The conducted testing showed that use of the controller 23 configured toprovide a model predictive control based oversight to the operations ofthe GPU 17 and/or plant 1 permitted the GPU 17 to operate with reducedmaximum and standard deviations of process variables while maintainingvalues of different operational set points within given safety and/orcapital assets preservation constraints for the different elements of aGPU 17. Reduced variance permits the GPU 17 to operate more efficientlyas losses associated with changes to steady state conditions can beavoided. Further, the improved operations of the GPU 17 was found tohelp improve the cost effectiveness of the carbon capture operations ofthe GPU 17 while maintaining the stability of control and safety ofoperation of the GPU 17 and plant 1.

It is contemplated that embodiments of the plant 1 and GPU 17 can beconfigured to improve carbon dioxide concentration (e.g. increase thecarbon dioxide content within the product) in the substantially carbondioxide product output by the GPU 17 for storage in the storage device19. Embodiments can also save on power consumed by operations of the GPU17 while maintaining a desired carbon dioxide capture rate provided bythe GPU 17. Embodiments can also be configured to prevent processconditions that can cause formation of dry ice and/or water ice fromoccurring while also improving the stability of operations, controlledresponse to deviations in the value of one or more DVs or otheroperations of the plant, and reduce deviations of process variables thatcan occur during transient upsets that may arise during GPU 17operations. Embodiments of the controller 23 can permit the GPU 17 tooperate such that the optimum operating point for the GPU at steadystate to produce liquid carbon dioxide product from the separation unit117 for sending to storage device 19 is achieved with highest puritywhile simultaneously maintaining a required minimum carbon capture ratewith the minimum consumption of power and/or minimum economic costassociated with operations of the GPU 17.

It should be appreciated that any of the above noted features of a plantsuch as an industrial plant or an energy production plant in anyparticular embodiment expressly discussed herein may be combined withother features or elements of other embodiments except when such acombination would be mutually exclusive or otherwise incompatibletherewith as may be appreciated by those of at least ordinary skill inthe art. It should also be appreciated that different variations to theabove discussed embodiments may be made to meet a particular set ofdesign criteria. For instance, a combustor can be configured as afurnace of a boiler unit that is configured to combust fuel in multiplecombustion zones. The furnace of such a boiler unit may include only oneburner or may include a plurality of spaced apart burners. As anotherexample, the composition of off gas from the separation unit 117 can beany of a number of suitable compositions that meet a particular set ofdesign criteria. As yet another example, heat exchangers, pumps, fans,valves, measurement sensors, conduit elements (e.g. tubes, pipes, ducts,vessels, etc.) and other elements may also be added to embodiments ofthe system to facilitate fluid movement or help control changes in theoperation of the system. As yet another example, an air separation unitmay be configured to provide oxygen or an oxidant air flow to acombustor of the energy production system. The air separation unit mayhave multiple storage tanks, such as multiple oxygen retaining vessels,for retaining oxygen gas or storing such gas until that gas is needed tobe fed to a boiler unit or a combustion unit.

While the invention has been described with reference to variousexemplary embodiments, it will be understood by those skilled in the artthat various changes can be made and equivalents can be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications can be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims.

What is claimed is:
 1. A method of operating a plant having a gasprocessing unit (GPU), comprising: determining parameter valuesassociated with operations of the GPU; utilizing the parameter valuesassociated with the operations of the GPU to determine biasing valuesfor biasing set points used to control operations of elements of theGPU; and sending the biasing values for adjusting the set points.
 2. Themethod of claim 1, comprising: adjusting the set points based upon thebiasing values using proportional-integral-derivative controllers thatmonitor operations of the GPU.
 3. The method of claim 1, comprising:determining the biasing values via the formula:J=Σ _(i=1) ^(N) ^(CV) α(CV_(i) ^(SP)−CV_(i) ^(PV))²+Σ_(j=1) ^(N) ^(CT)β(CT_(j) ^(lim)−CT_(j) ^(PV))²+Σ_(k=1) ^(N) ^(MV) γΔMV_(k) ² where,CV_(i) ^(SP): is a reference value of an i-th control variable, CV_(i)^(PV): is a measured value of the i-th control variable, CT_(j) ^(lim):is a limit of a j-th constraint variable, CT_(j) ^(PV): is a measuredvalue of the j-th constraint variable ΔMV_(k): is an actual change ofthe k-th biasing value, α: is a weighting coefficient reflectingrelative importance of the control variables, β: is a weightingcoefficient reflecting relative importance of the constraint variables,and γ: is a weighting coefficient penalizing changes of at least apre-specified value in biasing value.
 4. The method of claim 3, whereinthe plant is configured to generate electricity or power, and the methodcomprises: capturing, via the GPU, carbon dioxide from flue gas outputby a combustion unit of the plant.
 5. The method of claim 3, wherein:the control variables comprise: (i) carbon dioxide content of asubstantially carbon dioxide fluid to be sent from a separation unit ofthe GPU to a storage device, and (ii) a rate of capture of carbondioxide from the flue gas; and the constraint variables comprise: (i) anoff gas expander outlet temperature, (ii) an outlet temperature forsubstantially carbon dioxide liquid output from at least one separationcolumn of a separation unit of the GPU, and (iii) at least one flue gastemperature.
 6. The method of claim 3, wherein the biasing valuescomprise: (i) compressor inlet pressure set point values, (ii) off gasexpander temperature set point values, and (iii) at least one separationunit temperature set point value.
 7. The method of claim 3, comprising:determining at least one biasing value utilizing at least onedisturbance variable value.
 8. The method of claim 7, wherein thedisturbance variable value comprises: a flow rate of flue gas fed to theGPU.
 9. The method of claim 3, wherein values of the constraintvariables are selected to prevent formation of dry ice and water ice inthe GPU.
 10. An apparatus comprising: a gas processing unit (GPU); and acontroller having a processor connected to non-transitory memory, amodel predictive control program being stored in the memory; the GPUbeing configured to connect to a combustion unit such that flue gasemitted from the combustion unit will be fed to the GPU, the GPU beingconfigured to separate carbon dioxide from the flue gas to capture thecarbon dioxide from the flue gas; the controller being communicativelyconnected to the GPU to control operations of the GPU with the modelpredictive control program.
 11. The apparatus of claim 10, wherein themodel predictive control program is structured to configure thecontroller to determine parameter values associated with operations ofthe GPU, utilize the parameter values associated with the operations ofthe GPU to determine biasing values for biasing set points by whichoperations of elements of the GPU are controlled, and send thedetermined biasing values to the GPU for adjusting the set points whenthe model predictive control program is run by the controller.
 12. Theapparatus of claim 11, wherein the biasing values are determined by theformula:J=Σ _(i=1) ^(N) ^(CV) α(CV_(i) ^(SP)−CV_(i) ^(PV))²+Σ_(j=1) ^(N) ^(CT)β(CT_(j) ^(lim)−CT_(j) ^(PV))²+Σ_(k=1) ^(N) ^(MV) γΔMV_(k) ² where,CV_(i) ^(SP): is a reference value of an i-th control variable, CV_(i)^(PV): is a measured value of the i-th control variable, CT_(j) ^(lim):is a limit of a j-th constraint variable, CT_(j) ^(PV): is a measuredvalue of the j-th constraint variable ΔMV_(k): is an actual change ofthe k-th biasing value, α: is a weighting coefficient reflectingrelative importance of the control variables, β: is a weightingcoefficient reflecting relative importance of the constraint variables,and γ: is a weighting coefficient penalizing changes of at least apre-specified value in manipulated variables.
 13. The apparatus of claim12, wherein the GPU comprises: a cooling unit, a flue gas compressorsystem, a purification unit, a dryer unit, a condenser unit, and aseparation unit; the cooling unit being configured to receive flue gasemitted by the combustion unit to cool the flue gas to within apre-specified temperature; the flue gas compressor system beingconnected to the cooling unit to receive the cooled flue gas from thecooling unit, the flue gas compressor system being configured tocompress the flue gas to a pre-specified pressure; the purification unitbeing connected to the flue gas compressor system to receive thecompressed flue gas, the purification unit being configured to removeheavy metals from the flue gas; the dryer unit being connected to thepurification unit to receive the flue gas from the purification unit,the dryer unit being configured to remove water from the flue gas toreduce a dew point of the flue gas; the condenser unit being connectedto the dryer unit to receive the flue gas from the dryer unit, thecondenser unit being configured to condense carbon dioxide from the fluegas such that liquid carbon dioxide will be formed from the flue gas;and the separation unit being connected to the condenser to receive theflue gas and the liquid carbon dioxide from the condenser unit, theseparation unit being configured to separate the liquid carbon dioxidefrom the flue gas.
 14. The apparatus of claim 13, comprising: a storagedevice connected to the separation unit to receive a substantiallycarbon dioxide fluid from the separation unit.
 15. The apparatus ofclaim 13 in combination with a plant, the plant comprising: a combustionunit connected to the GPU of the apparatus; wherein the flue gasseparated from the liquid carbon dioxide will be an off gas; and theseparation unit being connected to the dryer unit such that the off gaswill be fed from the separation unit to the dryer unit as a drying fluidto pass through the dryer for removing water from the flue gas.